The present invention relates to a continuous-zoom imaging device of an interferometer and; more particularly, to a continuous-zoom imaging device, which can be widely applied to interference apparatuses, related measurement apparatuses utilizing the interference principle, related imaging devices of interference pattern, and common imaging devices.
An interferometer is an apparatus utilizing the interference phenomenon of light for measuring optical devices or other physical parameters. How to effectively obtain the interference pattern is thus an important issue of this kind of apparatus.
There are several kinds of interference systems, but their principle is very similar. With the commonly adopted Fizau type interferometer as an example, as shown in FIG. 1, an interferometer can be divided into two parts, one being a light projection system, the other being an interference pattern imaging system. Please refer to U.S. Pat. No. 4,201,473. The light projection system comprises a laser 10, a spatial filter 12, a splitter 14, a collimation device 16, a reference plane 18, and a test plane 20. In the interference pattern imaging system, reflected lights of the test plane 20 and the reference plane 18 interfere with each other to generate an interference pattern. The interference pattern passes through the collimation device 16, is vertically reflected by the splitter 14, then passes through a rotating diffuser 22, a zoom lens 24, and an attenuator 26, and is finally transmitted to a TV camera 28 to be read out. Therefore, the quality of the interference pattern depends on the imaging system.
In the imaging system of interferometer in prior art, the interference pattern is imaged on the rotating diffuser 22. The image on the rotating diffuser 22 is used as an object image of the zoom lens 24 and imaged on the focus plane of the camera 28. The function of the rotating diffuser 22 is to resolve the noise problem generated in optical paths of interferometer. Please refer to U.S. Pat. No. 4,201,473. The reason is that the interference pattern is not generated only on the reference plane 18 and the test plane 20. Dusts on an optical device like the splitter 14, the collimation device 16, or the spatial filter 12 will cause some trace reflection lights, which will generate some trace minor fringes, These noises are, and can be eliminated using the diffuser.
Moreover, the output power and coherent stability of the laser will generate time speckles, which will affect the stability of interference pattern. The diffuser can be used to average these noises. However, the diffuser itself is not perfectly flat so the laser light will generate space speckles on the plane to affect the quality of interference pattern. The diffuser must be rotated to resolve this problem by averaging in time and space. This way is the most commonly used method. But the rotating diffuser causes many problems described in detail below. The rotating diffuser will let the interference pattern not be directly imaged on a CCD, hence increasing noise of image and also reducing the transmittance of the diffuser and the modulation transform function (MTF). Because the image on the rotating diffuser is like a Lambertian surface, the phenomenon of vignetting will easily occur when the zoom lens forming the image on the CCD. This will bring about a very large difference between the brightness at the edge and the center of the interference image, resulting in difficulty in discrimination of image, as shown in FIG. 2. In order to improve this drawback, it is necessary to design a very high-end zoom lens, hence increasing the cost and being impractical. Furthermore, it is necessary to add a motor in the apparatus for driving the rotating diffuser to rotate. The coaxial stability of the motor is thus very important. Vibration caused by the motor will also affect the interference pattern.
It is necessary to add many components using the above conventional method, hence increasing the volume, weight, and cost and also difficulty in assembly. Please refer to U.S. Pat. Nos. 4,577,131 and 5,473,434. In order to keep a stable brightness of the interference pattern during the zooming process, it is necessary to add an attenuator for fine tuning. Most designs mainly adopt two-stage adjustment (the zoom lens 24 and the attenuator 26 are adjusted, respectively) without any joint device, hence resulting in complexity and variation in measurement. Accordingly, the present invention aims to propose a continuous-zoom imaging device of interferometer to resolve the above problems in the prior art.
The primary object of the present invention is to propose a continuous-zoom imaging device of an interferometer, which shortens the optical path of interference pattern and reduces disturbance of noise in the optical path, thereby improving the quality of interference pattern and thus obtaining a high-quality image of interference pattern.
Another object of the present invention is to provide a continuous-zoom imaging device of an interferometer without a rotating diffuser. The design without any motor overcomes the problems of coaxial stability and vibration and also has the advantages of shrunk volume, reduced number of components, lowered cost, and easy assembly.
Yet another object of the present invention is to provide a continuous-zoom imaging device of an interferometer, whose magnification ratio can be adjusted, and a joint attenuator can be matched to achieve the object of automatic adjustment of light.
Still yet another object of the present invention is to provide a continuous-zoom imaging device of an interferometer, which can extend the application range of apparatus, increase convenience in operation, and simultaneously reduce complexity in assembly of apparatus.
To achieve the above objects, the present invention comprises two planes, a collimation device, and a continuous-zoom device. Reflected lights of the two planes interfere with each other to generate an interference pattern. The collimation device converts a parallel light of the interference pattern into a convergent light, which passes through an adjustment means of optical path and is guided to a polarization beam splitter (PBS). The continuous-zoom device is used to adjust the magnification ratio of the interference pattern on the imaging passageway and to output an object image, which is then imaged onto a charge-coupled device (CCD).
The various objects and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with the appended drawings, in which: